1. Field of the Invention
The present invention relates generally to disposable hypodermic syringes. More particularly the invention relates to safety syringes wherein the hypodermic needle is retractable into the barrel of the syringe after use to prevent accidental needle prick. Most particularly the invention relates to a safety syringe which is automatically retracted into the barrel after use by a vacuum created within the barrel by movement of the plunger.
2. Related Art
Due to the recent advent of the AIDS virus, which may be contracted by contaminated hypodermic syringes, there have been several retractable needle hypodermic syringes invented and patented. The retraction of the needle into the barrel of the syringe after use reduces the risk of “needle prick”, or the accidental pricking of the person giving the injection after the syringe has been used.
The prior art discloses different syringes which accomplish the retraction. Some of the recently patented retractable needle syringes include U.S. Pat. No. 4,692,156 (Haller); U.S. Pat. No. 4,675,005 (DeLuccia); U.S. Pat. No. 4,747,830 (Gloyer, et al); U.S. Pat. No. 4,790,822 (Haining) and U.S. Pat. No. 4,950,251 (Haining). All of the syringes disclosed include a hypodermic needle mounted on a carrier which is slidable in the barrel. The plunger is locked to this carrier after the injection has been given and is withdrawn up into the barrel by withdrawal of the plunger. One disadvantage of the above syringes is that the locking mechanism takes up some space in the barrel of the syringe and may prevent all of the measured liquid from being ejected by the plunger. This problem is exacerbated in the very small syringes such as the 1 cc tuberculin type. The liquid left in the barrel may be a substantial portion of the measured dose. In addition the narrowness of the barrel of the 1 cc syringe makes it difficult to design a needle carrier and locking mechanism that will fit in the barrel without enlarging the diameter so much as to make the calibration useless.
Automatic retractable needle syringes have become more popular with the first syringes having springs which when released retract the needle into the barrel. One example of this type is U.S. Pat. No. 5,885,257 (Badger).
Vacuum powered retraction mechanisms are disclosed in U.S. Pat. No. 5,000,736 (Kaufhold et al) and U.S. Pat. No. 6,846,301 (Smith et al). In the first the vacuum, is provided in the syringe as shipped and breaking a seal activates the mechanism. In the second the vacuum is created by movement of the plunger within the barrel. The main drawback to the second invention is that the entire barrel has to be evacuated and the force applied over the entire cross sectional area is relatively small.